Constant term in the expansion of (1 + x*y + y*z + z*x + 1/(x*y*z))^n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =61a(6) =361a(7) =1261a(8) =3361a(9) =7561a(10) =34021a(11) =235621a(12) =1294921a(13) =5482621a(14) =19039021a(15) =65345281a(16) =286147681a(17) =1511480881a(18) =7688794681a(19) =34337600281a(20) =138221512741a(21) =554603041441